A Nonaqueous Redox Flow Battery Operating over an 80 Degrees Celsius Temperature Range

Abstract

Multi-redox electrolytes with redox potentials were evaluated in redox flow cells at -40, 25, 40 ºC and Cells operated at -40 ℃ were assembled with premixed electrolytes and a non-selective separator due to high impedance of the anion-selective membrane at -40 ºC. After 100 cycles at that temperature, cells were raised to room temperature and cycled, then to 40 ºC. This low temperature cell cycled stably though at room temperature for 9 cycles, despite an increase in capacity, the cell cycled with lower efficiency, which is presumably due to faster crossover at the higher temperature. Unlike room temperature cycling, the cell did not retain high capacity at 40 ºC. Active material decomposition is a plausible reason for lower capacity at elevated temperature. After the high temperature cycling, the cell was cycled for 9 cycles at room temperature to see if the capacity recovered, but the capacity remained similar as -40 and 40 ºC cycling with fading observed at this temperature. Post-cycling cyclic voltammetry shows some formation of byproducts in the high potential region, although their identity is unknown. This marks the first time that non-aqueous redox flow cells have been cycled at such low temperatures and over such a wide temperature range. Figure 1